Liquid crystal aligning agent composition, method for producing liquid crystal alignment film using same, and liquid crystal alignment film using same

ABSTRACT

The present invention relates to a liquid crystal aligning agent composition for producing a liquid crystal alignment film having improved film strength together with liquid crystal alignment properties, a method for producing a liquid crystal alignment film using the same, and a liquid crystal alignment film and a liquid crystal display device using the same.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. 371 National Phase Entry Applicationfrom PCT/KR2018/007240, filed Jun. 26, 2018, which claims priority toand the benefits of Korean Patent Application No. 10-2017-0083848 filedwith the Korean Intellectual Property Office on Jun. 30, 2017, thedisclosures of which are incorporated herein by reference in theirentirety.

The present invention relates to a liquid crystal aligning agentcomposition for producing a liquid crystal alignment film havingimproved film strength together with liquid crystal alignmentproperties, a method for producing a liquid crystal alignment film usingthe same, and a liquid crystal alignment film and a liquid crystaldisplay device using the same.

BACKGROUND ART

In a liquid crystal display device, a liquid crystal alignment filmplays a role of aligning liquid crystals in a certain direction.Specifically, a liquid crystal alignment film serves as a director inthe arrangement of liquid crystal molecules, and thus, when the liquidcrystals move by an electric field to form an image, it helps them tomove in an appropriate direction. Generally, in order to obtain uniformbrightness and a high contrast ratio in a liquid crystal display device,it is essential that the liquid crystals are uniformly aligned.

As a conventional method for aligning a liquid crystal, a rubbing methodof coating a polymer film such as a polyimide onto a substrate such asglass and rubbing the surface thereof in a predetermined direction usingfibers such as nylon or polyester has been used. However, the rubbingmethod may cause serious problems during manufacture of a liquid crystalpanel because fine dust or electrostatic discharge (ESD) may occur whenthe fiber and polymer film are rubbed.

In order to solve the problems of the rubbing method, a photo-alignmentmethod of inducing anisotropy in a polymer film by light irradiationrather than the rubbing, and aligning liquid crystals using theanisotropy, has been recently studied.

As materials that can be used for the photo-alignment method, variousmaterials have been introduced, among which polyimide is mainly used forvarious superior performances of liquid crystal alignment films.However, polyimide is usually poor in solubility in a solvent, so it isdifficult to apply it directly to a manufacturing process of forming analignment film by coating in a solution state. Accordingly, aftercoating in the form of a precursor such as a polyamic acid or a polyamicacid ester having excellent solubility, a high-temperature heattreatment process is performed to form polyimide, which is thensubjected to light irradiation to align liquid crystals. However, inorder to obtain sufficient liquid crystal alignment properties bysubjecting the film in the form of polyimide to light irradiation, notonly is a large amount of light irradiation energy required and so it isdifficult to secure actual productivity, but also there is a limitationin that an additional heat treatment process is required for securingalignment stability after the light irradiation.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

It is an object of the present invention to provide a liquid crystalaligning agent composition for producing a liquid crystal alignment filmhaving improved film strength together with liquid crystal alignmentproperties.

It is another object of the present invention to provide a method forproducing a liquid crystal alignment film using the above-describedliquid crystal aligning agent composition.

It is a further object of the present invention to provide a liquidcrystal alignment film prepared by the above-described productionmethod, and a liquid crystal display device including the same.

Technical Solution

In order to achieve the above objects, the present invention provides aliquid crystal aligning agent composition including: i) a first polymerfor a liquid crystal aligning agent including two or more repeatingunits selected from the group consisting of a repeating unit representedby the following Chemical Formula 1, a repeating unit represented by thefollowing Chemical Formula 2, and a repeating unit represented by thefollowing Chemical Formula 3, wherein the first polymer includes therepeating unit represented by Chemical Formula 1 in an amount of 5 to 74mol % with respect to a total of the repeating unit represented by thefollowing Chemical Formulae 1 to 3, ii) a second polymer for a liquidcrystal aligning agent including a repeating unit represented by thefollowing Chemical Formula 4, iii) a compound having two or more epoxygroups in a molecule, and iv) a phosphine-based compound represented bythe following Chemical Formula 5.

In Chemical Formulae 1 to 5,

at least one of R¹ and R² is a C₁₋₁₀ alkyl, and the other is hydrogen,

R³ and R⁴ are each independently hydrogen or a C₁₋₁₀ alkyl, and

X¹ is a tetravalent organic group represented by the following ChemicalFormula 6.

In Chemical Formula 6,

R⁵ to R⁸ are each independently hydrogen or a C₁₋₆ alkyl,

X², X³, and X⁴ are each independently a tetravalent organic groupderived from a hydrocarbon having 4 to 20 carbon atoms, a tetravalentorganic group in which at least one H in the tetravalent organic groupis substituted with a halogen, or at least one —CH₂— is replaced by —O—,—CO—, —S—, —SO—, —SO₂—, or —CONH— such that oxygen or sulfur atoms arenot directly linked, and

Y¹, Y², Y³, and Y⁴ are each independently a divalent organic grouprepresented by the following Chemical Formula 7.

In Chemical Formula 7,

R⁹ and R¹⁰ are each independently a halogen, a cyano, a C₁₋₁₀ alkyl, aC₂₋₁₀ alkenyl, a C₁₋₁₀ alkoxy, a C₁₋₁₀ fluoroalkyl, or a C₁₋₁₀fluoroalkoxy,

p and q are each independently an integer between 0 and 4, and

L¹ is a single bond, —O—, —CO—, —S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂—,—CONH—, —COO—, —(CH₂)_(z)—, —O(CH₂)_(z)O—, —O(CH₂)_(z)—,—OCH₂—C(CH₃)₂—CH₂O—, —COO—(CH₂)_(z)—OCO—, or —OCO—(CH₂)_(z)—COO—,

wherein z is an integer between 1 and 10,

m is an integer between 0 and 3, or between 1 and 3, and

A¹, A², and A³ are each independently hydrogen, or a C₁₋₂₀ alkyl, aC₃₋₂₀ cycloalkyl, a C₆₋₂₀ aryl, or a C₆₋₂₀ aryl substituted with atleast one C₁₋₂₀ alkyl group.

The liquid crystal aligning agent composition according to the presentinvention is characterized by including a compound having two or moreepoxy groups in a molecule, and a phosphine-based compound, togetherwith a first polymer for a liquid crystal aligning agent which is apartially imidized polyimide precursor, and a second polymer for aliquid crystal aligning agent, which is a general polyimide precursor.

When the existing polyimide is used as a liquid crystal alignment film,a polyimide precursor having excellent solubility, a polyamic acid orpolyamic acid ester, are coated and dried to form a coating film, whichis then converted into polyimide through a high-temperature heattreatment process, and then subjected to light irradiation to performalignment treatment. However, in order to obtain sufficient liquidcrystal alignment properties by subjecting the film in the form ofpolyimide to light irradiation, not only is a large amount of lightirradiation energy required, but also an additional heat treatmentprocess is undertaken for securing alignment stability after the lightirradiation. Since the large amount of light irradiation energy and theadditional high-temperature heat treatment process are verydisadvantageous in view of the process cost and process time, alimitation in applying it to actual mass production process existed.

In this regard, the present inventors found through experiments that,when the first polymer for a liquid crystal aligning agent whichessentially includes a repeating unit represented by Chemical Formula 1,and additionally includes at least one repeating unit selected from thegroup consisting of a repeating unit represented by Chemical Formula 2and a repeating unit represented by Chemical Formula 3, and the secondpolymer for a liquid crystal aligning agent including a repeating unitrepresented by Chemical Formula 4 are mixed and used, the first polymercontains a certain amount of already imidized imide repeating units, andthus it is possible to produce anisotropy by directly irradiating thelight without a heat treatment process after the formation of a coatingfilm, followed by conducting a heat treatment to complete the alignmentfilm, whereby not only can the light irradiation energy be significantlyreduced, but also a liquid crystal alignment film having excellentalignment properties and stability as well as excellent voltage holdingratio and electrical properties can be produced.

Further, the present inventors have found that in addition to thepolymers for liquid crystal aligning agents, when a compound having twoor more epoxy groups in a molecule is included in the liquid crystalaligning agent composition, a liquid crystal alignment film preparedtherefrom can not only exhibit a high voltage holding ratio but alsoenhance the alignment stability due to heat stress and the mechanicalstrength of the alignment film. Without wishing to be bound by anytheory, in the course of heat treatment after the production ofanisotropy by light irradiation, a thermal crosslinking reaction occursbetween the compound having an epoxy group and the carboxylic acid groupof the polyimide precursor or the partially imidized polymer, therebyincreasing the voltage holding ratio. In addition, since a compoundhaving two or more epoxy groups in a molecule is used, in particular,not only are these properties further improved, but also thecrosslinking reaction among the polyimide precursor or partiallyimidized polymer chains can occur, thereby improving the alignmentstability and the mechanical strength of the alignment film.

In particular, it has been found through experiments by the presentinventors that according to the present invention, as a phosphine-basedcompound represented by the following Chemical Formula 5 is added in theliquid crystal aligning agent composition, a thermal crosslinkingreaction between the compound having two or more epoxy groups in amolecule and the polymer for a liquid crystal aligning agent can beaccelerated to further increase the effects of improving the alignmentstability and the mechanical strength of the alignment film, therebycompleting the present invention.

in Chemical Formula 5, A¹, A², and A³ are each independently hydrogen, aC₁₋₂₀ alkyl, a C₃₋₂₀ cycloalkyl, C₆₋₂₀ aryl, or a C₆₋₂₀ aryl substitutedwith at least one C₁₋₂₀ alkyl group.

The phosphine-based compound represented by Chemical Formula 5 is addedas a reaction accelerator for enhancing the thermal crosslinkingreactivity between the compound having two or more epoxy groups in themolecule and the polymer for a liquid crystal aligning agent. Thus, thereactivity of the compound having two or more epoxy groups in themolecule is remarkably improved as compared with the reactivity beforethe addition, and also a stronger crosslinked structure between thepolymer for a liquid crystal aligning agent and the compound having twoor more epoxy groups in the molecule is formed in the finally producedalignment film, thereby increasing the mechanical strength of thealignment film.

In addition, as the phosphine-based compound represented by ChemicalFormula 5 does not affect the imidization reaction by sintering of thepolymer for a liquid crystal aligning agent contained in thecomposition, the alignment properties of the finally produced alignmentfilm were found to be equal to or higher than the conventional level.

As described above, the effect due to the phosphine-based compound inthe present invention is not achieved by simply adding it to the liquidcrystal aligning agent composition, but when that compound is containedin the liquid crystal aligning agent composition together with thecompound having two or more epoxy groups in a molecule, it is achievedby an organic reaction or bonding between the compound having two ormore epoxy groups in the molecule and the phosphine-based compound.

Further, generally, in the field of liquid crystal alignment films,since the mechanical strength and alignment properties of the alignmentfilm have a trade-off relationship, it is a key goal of research anddevelopment that all of these properties are improved to an appropriatelevel or higher. Thus, the effect realized by the liquid crystalaligning agent composition of the one embodiment appears to beremarkable compared to the state of the art.

Hereinafter, the present invention will be described in more detail.

Definition of Terms

Unless specified otherwise herein, the following terms can be defined asfollows.

Throughout the specification, when one part “includes” one constituentelement, unless otherwise specifically described, this does not meanthat another constituent element is excluded, but means that anotherconstituent element may be further included.

As used herein, the term “substituted” means that a hydrogen atom bondedto a carbon atom in a compound is changed into another substituent, anda position to be substituted is not limited as long as the position is aposition at which the hydrogen atom is substituted, that is, a positionat which the substituent may be substituted, and when two or more aresubstituted, the two or more substituents may be the same as ordifferent from each other.

In the present specification, the C₄₋₂₀ hydrocarbon may be a C₄₋₂₀alkane, a C₄₋₂₀ alkene, a C₄₋₂₀ alkyne, a C₄₋₂₀ cycloalkane, a C₄₋₂₀cycloalkene, a C₆₋₂₀ arene, or a fused ring in which at least one cyclichydrocarbon among them shares two or more atoms, or a hydrocarbon towhich at least one hydrocarbon among them is chemically bonded.

Specifically, examples of the C₄₋₂₀ hydrocarbon may include n-butane,cyclobutane, 1-methylcyclobutane, 1,3-dimethylcyclobutane,1,2,3,4-tetramethylcyclobutane, cyclopentane, cyclohexane, cycloheptane,cyclooctane, cyclohexene, 1-methyl-3-ethylcyclohexene, bicyclohexyl,benzene, biphenyl, diphenylmethane, 2,2-diphenylpropane,1-ethyl-1,2,3,4-tetrahydronaphthalene, 1,6-diphenylhexane, etc.

In the present specification, the C₁₋₁₀ alkyl group may be astraight-chain, branched-chain, or cyclic alkyl group. Specifically, theC₁₋₁₀ alkyl group may be a straight-chain C₁₋₁₀ alkyl group; astraight-chain C₁₋₅ alkyl group; a branched-chain or cyclic C₃₋₁₀ alkylgroup; or a branched-chain or cyclic C₃₋₆ alkyl group. Morespecifically, examples of the C₁₋₁₀ alkyl group may include a methylgroup, an ethyl group, an n-propyl group, an iso-propyl group, ann-butyl group, an iso-butyl group, a tert-butyl group, an n-pentylgroup, an iso-pentyl group, a neo-pentyl group, a cyclohexyl group, etc.

In the present specification, the C₁₋₁₀ alkoxy group may be astraight-chain, branched-chain, or cyclic alkoxy group. Specifically,the C₁₋₁₀ alkoxy group may be a straight-chain C₁₋₁₀ alkoxy group; astraight-chain C₁₋₅ alkoxy group; a branched-chain or cyclic C₃₋₁₀alkoxy group; or a branched-chain or cyclic C₃₋₆ alkoxyl group. Morespecifically, examples of the C₁₋₁₀ alkoxy group may include a methoxygroup, an ethoxy group, an n-propoxy group, an iso-propoxy group, ann-butoxy group, an iso-butoxy group, a tert-butoxy group, an n-pentoxygroup, an iso-pentoxy group, a neo-pentoxy group, a cycloheptoxy group,etc.

In the present specification, the C₁₋₁₀ fluoroalkyl group may be a groupin which at least one hydrogen in the C₁₋₁₀ alkyl group is substitutedwith fluorine, and the C₁₋₁₀ fluoroalkoxy group may be a group in whichat least one hydrogen in the C₁₋₁₀ alkoxy group is substituted withfluorine.

In the present specification, the C₂₋₁₀ alkenyl group may be astraight-chain, branched-chain or cyclic alkenyl group. Specifically,the C₂₋₁₀ alkenyl group may be a straight-chain C₂₋₁₀ alkenyl group, astraight-chain C₂₋₅ alkenyl group, a branched-chain C₃₋₁₀ alkenyl group,a branched-chain C₃₋₆ alkenyl group, a cyclic C₅₋₁₀ alkenyl group, or acyclic C₆₋₈ alkenyl group. More specifically, examples of the C₂₋₁₀alkenyl group may include an ethenyl group, a propenyl group, a butenylgroup, a pentenyl group, a cyclohexenyl group, etc.

In the present specification, the aryl group is not particularlylimited, but preferably has 6 to 60 carbon atoms, and may be amonocyclic aryl group or a polycyclic aryl group. According to oneembodiment, the aryl group has 6 to 30 carbon atoms. According to oneembodiment, the aryl group has 6 to 20 carbon atoms. The aryl group maybe a phenyl group, a biphenyl group, a terphenyl group, or the like asthe monocyclic aryl group, but is not limited thereto. Examples of thepolycyclic aryl group include a naphthyl group, an anthracenyl group, aphenanthryl group, a pyrenyl group, a perylenyl group, a chrycenylgroup, a fluorenyl group, or the like, but is not limited thereto.

The halogen may be fluorine (F), chlorine (Cl), bromine (Br), or iodine(I).

As used herein, the term “phosphine-based compound” may refer to aphosphine compound, a phosphine compound substituted with an organicfunctional group, or a derivative compound thereof. The phosphinecompound is a compound having a molecular formula of PH₃, and thephosphine compound substituted with an organic functional group refersto a compound in which at least one organic functional group issubstituted at the position of hydrogen in the phosphine compound.

The multivalent organic group derived from an arbitrary compound refersto a residue in which a plurality of hydrogen atoms bonded to thearbitrary compound are removed. In one example, a tetravalent organicgroup derived from cyclobutane refers to a residue in which any fourhydrogen atoms bonded to cyclobutane are removed.

In the present specification, the notation

in the chemical formula refers to a residue in which hydrogens at therelevant site are removed. For example, the notation

refers to a residue in which four hydrogen atoms bonded to carbonnumbers 1, 2, 3, and 4 of cyclobutane are removed, that is, it refers toany one of tetravalent organic groups derived from cyclobutane.

Polymer for Liquid Crystal Aligning Agent

The liquid crystal aligning agent composition may include, as a polymerfor a liquid crystal aligning agent, i) a first polymer for a liquidcrystal aligning agent including two or more repeating units selectedfrom the group consisting of a repeating unit represented by ChemicalFormula 1, a repeating unit represented by Chemical Formula 2, and arepeating unit represented by Chemical Formula 3, wherein the firstpolymer includes the repeating unit represented by Chemical Formula 1 inan amount of 5 to 74 mol % with respect to all repeating unitsrepresented by Chemical Formulae 1 to 3, and ii) a second polymer for aliquid crystal aligning agent including a repeating unit represented byChemical Formula 4.

In the repeating units of Chemical Formulae 1 to 4, X¹ is a tetravalentorganic group represented by Chemical Formula 6, and X² to X⁴ are eachindependently a tetravalent organic group derived from a hydrocarbonhaving 4 to 20 carbon atoms, a tetravalent organic group in which atleast one H in the tetravalent organic group is substituted with ahalogen, or at least one —CH₂— is replaced by —O—, —CO—, —S—, —SO—,—SO₂—, or —CONH— such that oxygen or sulfur atoms are not directlylinked.

In one example, X² to X⁴ may each independently be a tetravalent organicgroup represented by the following Chemical Formula 8.

In Chemical Formula 8,

R¹¹ to R¹⁴ are each independently hydrogen or a C₁₋₆ alkyl, and L² is aSingle bond, —O—, —CO—, —S—, —C(CH₃)₂—, —C(CF₃)₂—, —CONH—, —COO—,—(CH₂)_(z)—, —O(CH₂)_(z)O—, or —COO—(CH₂)_(z)—OCO—, wherein z is aninteger between 1 to 10.

On the other hand, Y¹ to Y⁴ are defined as a divalent organic grouprepresented by Chemical Formula 7, which can provide a polymer for aliquid crystal aligning agent having various structures capable ofexhibiting the above-described effects.

In Chemical Formula 7, hydrogen is bonded to a carbon which is notsubstituted with R⁹ or R¹⁰, and when p or q is an integer of 2 to 4, aplurality of R⁹ or R¹⁰ may be the same as or different from each other.Further, in Chemical Formula 7, m may be an integer of 0 to 3, or aninteger of 0 or 1.

Specifically, the first polymer for a liquid crystal aligning agent mayinclude the repeating unit represented by Chemical Formula 1, which isan imide repeating unit, in an amount of 10 mol % to 74 mol %, or 20 mol% to 60 mol %, based on all repeating units, among the repeating unitsrepresented by Chemical Formula 1, Chemical Formula 2, and ChemicalFormula 3. As described above, when the first polymer for a liquidcrystal aligning agent which includes a specific amount of the imiderepeating unit represented by Chemical Formula 1 is used, the polymerincludes a certain amount of already imidized imide repeating units, andthus, a liquid crystal alignment film having excellent alignmentproperties and stability as well as excellent voltage holding ratio andelectrical properties can be produced even when the high-temperatureheat treatment process is omitted and light is directly irradiated. Ifthe repeating unit represented by Chemical Formula 1 is included at lessthan the content range, sufficient alignment properties may not beexhibited and alignment stability may be deteriorated. On the contrary,if the content of the repeating unit represented by Chemical Formula 1exceeds the above content range, the solubility is lowered, and thus itmay be difficult to prepare a stable alignment solution capable ofcoating, which is problematic. Accordingly, it is preferable to includethe repeating unit represented by Chemical Formula 1 within theabove-mentioned content range, because it can provide a polymer for aliquid crystal aligning agent having excellent storage stability,electrical properties, alignment properties, and alignment stability.

Further, the first polymer for a liquid crystal aligning agent mayinclude the repeating unit represented by Chemical Formula 2 or therepeating unit represented by Chemical Formula 3 in an appropriateamount depending on the desired characteristics. Specifically, therepeating unit represented by Chemical Formula 2 may be included in anamount of 0 mol % to 40 mol %, 0 mol % to 30 mol %, or 0.1 mol % to 30mol %, based on all repeating units represented by Chemical Formulae 1to 3. The repeating unit represented by Chemical Formula 2 has a lowimide conversion rate during the high-temperature heat treatment processafter the light irradiation, and thus if the above range is exceeded,the overall imidization rate is insufficient, thereby deteriorating thealignment stability. Accordingly, the repeating unit represented byChemical Formula 2 exhibits appropriate solubility within theabove-mentioned range and thus can provide a polymer for a liquidcrystal aligning agent which can implement a high imidization rate,while having excellent processing properties.

Moreover, in the first polymer for a liquid crystal aligning agent, therepeating unit represented by Chemical Formula 3 may be included in anamount of 0 mol % to 95 mol %, or 10 mol % to 90 mol %, based on allrepeating units represented by Chemical Formulae 1 to 3. Within such arange, excellent coating properties can be exhibited, thereby providinga polymer for a liquid crystal aligning agent which can implement a highimidization rate, while having excellent processing properties.

Meanwhile, the second polymer for a liquid crystal aligning agent ismixed with the first polymer for a liquid crystal aligning agent, whichis a partially imidized polymer, and used as a liquid crystal aligningagent, and thus can significantly enhance the electrical properties ofan alignment film such as voltage holding ratio as compared to the casewhere only the first polymer for a liquid crystal aligning agent isused.

In order to exhibit such an effect, it is preferable that X⁴ in therepeating unit represented by Chemical Formula 4 is derived from anaromatic structure in view of improving the voltage holding ratio.

In addition, in the repeating unit represented by Chemical Formula 4, itis preferable that Y⁴ is a bivalent organic group represented byChemical Formula 7. Herein R⁹ and R¹⁰ are each independently ashort-chain functional group having 3 or less carbon atoms, or it ismore preferable that R⁹ and R¹⁰, which are branched structures, are notincluded (p and q are 0).

Preferably, the X², X³, and X⁴ are each independently a tetravalentorganic group represented by the following Chemical Formula 8.

In Chemical Formula 8,

R¹¹ to R¹⁴ are each independently hydrogen, or a C₁₋₆ alkyl, and

L² is a single bond, —O—, —CO—, —S—, —C(CH₃)₂—, —C(CF₃)₂—, —CONH—,—COO—, —(CH₂)_(z)—, —O(CH₂)_(z)O—, or —COO—(CH₂)_(z)—OCO—, wherein z isan integer between 1 and 10.

Further, the first polymer for a liquid crystal aligning agent and thesecond polymer for a liquid crystal aligning agent may be mixed in aweight ratio of 1:9 to 9:1, 15:85 to 85:15, or 2:8 to 8:2. As describedabove, the first polymer for a liquid crystal aligning agent contains acertain amount of already imidized imide repeating units, and thus it ispossible to produce anisotropy by directly irradiating the light withouta high-temperature heat treatment process after the formation of thecoating film, followed by conducting a heat treatment to complete thealignment film. The second polymer for a liquid crystal aligning agentcan enhance the electrical properties such as voltage holding ratio.When the first polymer for a liquid crystal aligning agent and thesecond polymer for a liquid crystal aligning agent having suchcharacteristics are mixed in the weight ratio range above and used,excellent photo-reaction characteristics and liquid crystal alignmentproperties that the first polymer for a liquid crystal aligning agenthas and excellent electrical properties that the second polymer for aliquid crystal aligning agent has can complement each other, and thus aliquid crystal alignment film simultaneously having excellent alignmentproperties and electrical properties can be produced.

Compound Having Two or More Epoxy Groups in a Molecule

In addition to the polymers for liquid crystal aligning agents describedabove, the liquid crystal aligning agent composition of the presentinvention includes a compound having two or more epoxy groups in amolecule, thereby allowing a liquid crystal alignment film preparedtherefrom to exhibit a high voltage holding ratio.

The molecular weight of the compound having two or more epoxy groups ina molecule may preferably be 100 g/mol to 10,000 g/mol. In the presentspecification, the molecular weight means a weight average molecularweight in terms of polystyrene measured by the GPC method. In theprocess of determining the weight average molecular weight in terms ofpolystyrene measured by the GPC method, a commonly known analyzingdevice, a detector such as a refractive index detector, and ananalytical column can be used. Commonly applied conditions fortemperature, solvent, and flow rate can be used. Specific examples ofthe measurement conditions include a temperature of 30° C., a chloroformsolvent, and a flow rate of 1 mL/min.

As the compound having two or more epoxy groups in a molecule, acycloaliphatic-based epoxy, a bisphenol-based epoxy, or a novolac-basedepoxy can be used. As a specific example, (3′,4′-epoxycyclohexane)methyl3,4-epoxycyclohexylcarboxylate, 4,4′-methylene bis(N,N′-diglycidylaniline), or2,2′-(3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl)bis(oxy)bis(methylene)dioxiranecan be used.

In addition, the compound having two or more epoxy groups in themolecule is preferably included in an amount of 0.1 to 30 parts byweight based on a total of 100 parts by weight of the first polymer fora liquid crystal aligning agent and the second polymer for a liquidcrystal aligning agent.

Phosphine-Based Compound

In addition to the polymers for a liquid crystal aligning agent and thecompound having two or more epoxy groups in a molecule described above,the liquid crystal aligning agent composition of the present inventionincludes a phosphine-based compound, thereby allowing a liquid crystalalignment film prepared therefrom to exhibit high mechanical strength.

The phosphine-based compound may have a structure represented byChemical Formula 5. In Chemical Formula 5, A¹, A², and A³ are eachindependently hydrogen, a C₁₋₂₀ alkyl, a C₃₋₂₀ cycloalkyl, a C₆₋₂₀ aryl,or a C₆₋₂₀ aryl substituted with at least one C₁₋₂₀ alkyl group. Morepreferably, in Chemical Formula 5, A¹, A², and A³ all may be hydrogen ora C₁₋₃ alkyl. Examples of the C₁₋₃ alkyl include methyl, ethyl, andpropyl.

As a specific example of the phosphine-based compound, phosphine (PH₃),or trimethyl phosphine may be used.

The phosphine-based compound is preferably included in an amount of 0.03to 30 parts by weight, 0.1 to 20 parts by weight, 1 to 10 parts byweight, or 3 to 7 parts by weight, based on a total of 100 parts byweight of the first polymer for the liquid crystal aligning agent andthe second polymer for the liquid crystal aligning agent.

Method for Producing Liquid Crystal Alignment Film

In addition, the present invention provides a method for producing aliquid crystal alignment film including the steps of: 1) coating theliquid crystal aligning agent composition onto a substrate to form acoating film; 2) drying the coating film; 3) subjecting the coating filmto alignment treatment immediately after the drying step; and 4)heat-treating and curing the alignment-treated coating film.

When an existing polyimide is used as a liquid crystal alignment film, apolyimide precursor having excellent solubility, and polyamic acid or apolyamic acid ester, are coated and dried to form a coating film, whichis then converted into polyimide through a high-temperature heattreatment process, and then subjected to light irradiation to performalignment treatment. However, in order to obtain sufficient liquidcrystal alignment properties by subjecting the film in the form of apolyimide to light irradiation, not only is a large amount of lightirradiation energy required, but also an additional heat treatmentprocess is undertaken for securing alignment stability after the lightirradiation. Since the large amount of light irradiation energy and theadditional high-temperature heat treatment process are verydisadvantageous in view of the process cost and process time, alimitation in applying it to actual mass production process existed.

In this regard, the present inventors found through experiments that,when a polymer including two or more repeating units selected from thegroup consisting of a repeating unit represented by Chemical Formula 1,a repeating unit represented by Chemical Formula 2, and a repeating unitrepresented by Chemical Formula 3, and particularly including therepeating unit represented by Chemical Formula 1 among theabove-described repeating units in an amount of 5 to 74 mol % is used,the polymer contains a certain amount of already imidized imiderepeating units, and thus it is possible to produce anisotropy bydirectly irradiating the light without a heat treatment process afterthe formation of a coating film, followed by conducting a heat treatmentto complete the alignment film, and thereby, not only can the lightirradiation energy be significantly reduced, but also a liquid crystalalignment film having enhanced alignment properties and stability can beproduced even by a simple process including one heat treatment step,thereby completing the present invention.

Hereinafter, the present invention will be described in detail for eachstep.

1) Coating the liquid crystal aligning agent composition onto asubstrate to form a coating film (Step 1)

Step 1 is a step of coating the liquid crystal aligning agent onto asubstrate to form a coating film.

The liquid crystal aligning agent composition includes i) a firstpolymer for a liquid crystal aligning agent including two or morerepeating units selected from the group consisting of a repeating unitrepresented by Chemical Formula 1, a repeating unit represented byChemical Formula 2, and a repeating unit represented by Chemical Formula3, wherein the first polymer includes the repeating unit represented byChemical Formula 1 in an amount of 5 to 74 mol % with respect to allrepeating unit represented by Chemical Formulae 1 to 3, ii) a secondpolymer for a liquid crystal aligning agent including a repeating unitrepresented by Chemical Formula 4, iii) a compound having two or moreepoxy groups in a molecule, and iv) a phosphine-based compoundrepresented by Chemical Formula 5. The details of the liquid crystalaligning agent composition are the same as the contents described above.

Meanwhile, the method of coating the liquid crystal aligning agentcomposition onto a substrate is not particularly limited, and forexample, a method such as screen printing, offset printing, flexographicprinting, inkjet printing, and the like can be used.

Further, the liquid crystal aligning agent composition may be acomposition in which the first polymer for a liquid crystal aligningagent, the second polymer for a liquid crystal aligning agent, thecompound having two or more epoxy groups in a molecule, and thephosphine-based compound are dissolved or dispersed in an organicsolvent. Specific examples of the organic solvent includeN,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone,N-vinylpyrrolidone, dimethylsulfoxide, tetramethylurea, pyridine,dimethyl sulfone, hexamethyl sulfoxide, γ-butyrolactone,3-methoxy-N,N-dimethylpropanamide, 3-ethoxy-N,N-dimethylpropanamide,3-butoxy-N,N-dimethylpropanamide, 1,3-dimethyl-imidazolidinone, ethylamyl ketone, methyl nonyl ketone, methyl ethyl ketone, methyl isoamylketone, methyl isopropyl ketone, cyclohexanone, ethylene carbonate,propylene carbonate, diglyme, 4-hydroxy-4-methyl-2-pentanone, ethyleneglycol monomethyl ether, ethylene glycol monomethyl ether acetate,ethylene glycol monoethyl ether, ethylene glycol monoethyl etheracetate, ethylene glycol monopropyl ether, ethylene glycol monopropylether acetate, ethylene glycol monoisopropyl ether, ethylene glycolmonoisopropyl ether acetate, ethylene glycol monobutyl ether, ethyleneglycol monobutyl ether acetate, and the like. They can be used alone orin combination of two or more.

In addition, the liquid crystal aligning agent composition may furtherinclude other components in addition to the polymer for a liquid crystalaligning agent and the organic solvent. In a non-limiting example, whenthe liquid crystal aligning agent composition is coated, additivescapable of improving the uniformity of the thickness of a film and thesurface smoothness, improving the adhesion between a photo-alignmentfilm and a substrate, changing the dielectric constant and conductivityof a photo-alignment film, or increasing the denseness of aphoto-alignment film may be further included. Examples of such additivesinclude various kinds of solvents, surfactants, silane-based compounds,dielectrics, crosslinking compounds, etc.

2) Drying the coating film (Step 2)

Step 2 is a step of drying the coating film prepared in Step 1.

The step of drying the coating film is for removing solvent or the likeused in the liquid crystal aligning agent composition, and for example,a method such as heating of a coating film or vacuum evaporation may beused. The drying may be preferably performed at a temperature of 50° C.to 130° C., or at a temperature of 70° C. to 120° C.

3) Subjecting the coating film to alignment treatment immediately afterthe drying step (Step 3)

Step 3 is a step of irradiating the coating film dried in Step 2 withlight or rubbing the coating film to perform alignment treatment.

In the present specification, the “coating film immediately after thedrying step” refers to irradiating the light immediately after thedrying step without carrying out a heat treatment at a temperature ofhigher than that of the drying step, and steps other than the heattreatment can be added.

More specifically, when a liquid crystal alignment film is producedusing a conventional liquid crystal alignment agent including polyamicacid or a polyamic acid ester, it includes a step of irradiating lightafter essentially performing a high-temperature heat treatment forimidization of polyamic acid. However, when a liquid crystal alignmentfilm is produced using the liquid crystal alignment agent of the oneembodiment described above, it does not include the heat treatment step,and light is directly irradiated to perform alignment treatment, andthen the alignment-treated coating film is cured by a heat treatment,thereby enabling production of a liquid crystal alignment film havingsufficient alignment property and enhanced stability even under lowlight irradiation energy.

In the alignment treatment step, the light irradiation is performed byirradiating polarized ultraviolet rays having a wavelength of 150 nm to450 nm. In this case, the intensity of the light exposure may varydepending on the kind of the polymer for a liquid crystal aligningagent, and preferably energy of 10 mJ/cm² to 10 J/cm² or energy of 30mJ/cm² to 2 J/cm² may be irradiated.

As for the ultraviolet rays, polarized ultraviolet rays selected amongthe ultraviolet rays subjected to polarization treatment by a method ofpassing through or reflecting with a polarizing device using a substratein which a dielectric anisotropic material is coated on the surface of atransparent substrate such as quartz glass, soda lime glass, sodalime-free glass, etc., a polarizer plate on which aluminum or metalwires are finely deposited, or a Brewster's polarizing device using thereflection of quartz glass, etc., are irradiated to perform thealignment treatment. Herein, the polarized ultraviolet rays may beirradiated perpendicularly to the surface of the substrate, or may beirradiated by forming an angle of incidence toward a specific angle. Bythis method, the alignment ability of the liquid crystal molecules isimparted to the coating film.

Further, in the alignment treatment step, a rubbing treatment can use amethod using a rubbing cloth. More specifically, in the rubbingtreatment, the surface of the coating film after the heat treatment stepcan be rubbed in one direction while rotating a rubbing roller in whicha rubbing cloth is attached to a metal roller.

4) Heat-treating the alignment-treated coating film (Step 4)

Step 4 is a step of heat-treating the coating film alignment-treated inStep 3.

The heat treatment may be performed by a heating means such as a hotplate, a hot air circulation path, an infrared ray furnace, and thelike, and the heat treatment is preferably performed at a temperature of100° C. to 300° C.

Meanwhile, Step 4 may include 4-1) a step of subjecting thealignment-treated coating film to a low-temperature heat treatment at200° C. or less; and 4-2) a step of heat-treating and curing theheat-treated coating film at a temperature higher than that of thelow-temperature heat treatment.

Generally, it is known that when an epoxy material is contained in aliquid crystal aligning agent, the strength and high voltage holdingratio of an alignment film are enhanced, and that the degree thereofincreases as the content of the epoxy material increases. However, whenthe content of the epoxy material increases, there is a problem that thehigh-temperature AC brightness fluctuation rate of a liquid crystal cellincreases. The reason why the high-temperature AC brightness fluctuationcharacteristics are deteriorated is not theoretically limited, but it isattributed to the fact that the alignment of the liquid crystal aligningagent and the epoxy reaction are performed simultaneously as thealignment of the liquid crystal aligning agent is performed at a hightemperature.

Accordingly, the liquid crystal aligning agent composition is coatedonto a substrate and dried to form a coating film, and then directlyirradiated with linearly polarized light without an imidization process,to induce initial anisotropy, and then a part of the alignment film isreoriented through a low-temperature heat treatment to stabilizedecomposition products. Subsequently, while performing ahigh-temperature heat treatment at a temperature higher than that of thelow-temperature heat treatment to progress the imidization, thealignment stabilization by the epoxy reaction can be achieved at thesame time. Accordingly, there are advantages in that, as the initialanisotropy progresses without an epoxy reaction, the content of theepoxy material can be increased while the alignment is effectivelyperformed.

The liquid crystal alignment film prepared according to the method forproducing a liquid crystal alignment film as described above ischaracterized by not only exhibiting excellent alignment properties, butalso exhibiting an excellent high-temperature AC brightness fluctuationratio and maintaining a high voltage holding ratio for a long time.

Specifically, since the initial anisotropy was induced by directlyirradiating linearly polarized light without an imidization process inStep 3, Step 4-1 is a step of reorienting a part of the alignment filmand stabilizing decomposition products through a low-temperature heattreatment. Further, such a low-temperature heat treatment step isdistinguished from a step of heat-treating and curing thealignment-treated coating film which will be described later.

The temperature for the low-temperature heat treatment is a temperaturecapable of reorienting a part of the alignment film and stabilizingdecomposition products without curing the coating film, and ispreferably 200° C. or lower. Alternatively, the temperature for thelow-temperature heat treatment is 110° C. to 200° C., or 130° C. to 180°C. Herein, the means of the heat treatment is not particularly limited,and may be performed by a heating means such as a hot plate, a hot aircirculation path, an infrared ray furnace, and the like.

Step 4-2 is a step of subjecting the coating film, which has beensubjected to a low-temperature heat-treated in Step 4-1, to a hightemperature-heat treatment to cure it.

The step of heat-treating and curing the alignment-treated coating filmis a step that is performed after the irradiation of light even in theconventional method for producing a liquid crystal alignment film usinga polymer for a liquid crystal aligning agent including a polyamic acidor polyamic acid ester, and is distinguished from the heat treatmentstep which is performed for coating the liquid crystal aligning agentcomposition onto a substrate and then performing imidization of theliquid crystal aligning agent composition before irradiating the lightor while irradiating the light.

In addition, the epoxy reaction of the compound having two or more epoxygroups in a molecule is performed during the heat treatment, and thusthe alignment stability can be improved. Accordingly, the temperaturefor the heat treatment is a temperature at which the imidization of thepolymer for a liquid crystal aligning agent and the epoxy reaction ofthe compound having two or more epoxy groups in a molecule areperformed, and is preferably higher than the temperature for thelow-temperature heat treatment of Step 4-1. The heat treatment of Step4-2 is preferably performed at a temperature of 200° C. to 250° C., orat a temperature of 210° C. to 240° C. In this case, the means of theheat treatment is not particularly limited and may be performed by aheating means such as a hot plate, a hot air circulation path, aninfrared ray furnace, and the like.

Liquid Crystal Alignment Film

Further, the present invention may provide a liquid crystal alignmentfilm prepared in accordance with the method for producing a liquidcrystal alignment film described above. Specifically, the liquid crystalalignment film may include an aligned cured product of the liquidcrystal aligning agent composition of the one embodiment. The alignedcured product means a material obtained through an alignment step and acuring step of the liquid crystal aligning agent composition of the oneembodiment.

As described above, when the first polymer for a liquid crystal aligningagent and the second polymer for a liquid crystal aligning agent aremixed and used, a liquid crystal alignment film having enhancedalignment properties and stability can be prepared. Furthermore, thealignment stability can be enhanced through the epoxy reaction of thecompound having two or more epoxy groups in a molecule.

Further, in the liquid crystal alignment film, the epoxy reaction of thecompound having two or more epoxy groups in the molecule is acceleratedby the phosphine-based compound, and thereby the film strength of thefinally produced liquid crystal alignment film can be improved.

The thickness of the liquid crystal alignment film is not particularlylimited, but for example, it can be freely adjusted within the range of0.001 μm to 100 μm. If the thickness of the liquid crystal alignmentfilm increases or decreases by a specific value, the physical propertiesmeasured in the alignment film may also change by a certain value.

Liquid Crystal Display Device

In addition, the present invention provides a liquid crystal displaydevice including the liquid crystal alignment film described above.

The liquid crystal alignment film may be introduced into a liquidcrystal cell by a known method, and likewise, the liquid crystal cellmay be introduced into a liquid crystal display device by a knownmethod. The liquid crystal alignment film can be prepared by mixing thepolymer essentially including the repeating unit represented by ChemicalFormula 1 and the polymer including the repeating unit represented byChemical Formula 4, thereby achieving excellent stability together withexcellent physical properties. Accordingly, a liquid crystal displaydevice which can exhibit high reliability is provided.

Advantageous Effects

According to the present invention, a liquid crystal aligning agentcomposition for producing a liquid crystal alignment film havingimproved film strength together with liquid crystal alignmentproperties, a method for producing a liquid crystal alignment film usingthe same, and a liquid crystal alignment film and a liquid crystaldisplay device using the same can be provided.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The prevention invention will be described in more detail by way ofexamples. However, these examples are given for illustrative purposesonly, and the scope of the invention is not intended to be limited bythese examples.

Production Example 1: Synthesis of Diamine Production Example 1-1)Synthesis of Diamine DA-1

Diamine DA-1 was synthesized according to the following reaction scheme.

Specifically, 1,3-dimethylcyclobuthane-1,2,3,4-tetracarboxylicdianhydride (DMCBDA) and 4-nitroaniline were dissolved in DMF(dimethylformamide) to prepare a mixture. Then, the mixture was reactedat about 80° C. for about 12 hours to prepare an amic acid.Subsequently, the amic acid was dissolved in DMF, and acetic anhydrideand sodium acetate were added thereto to prepare a mixture. Then, theamic acid contained in the mixture was imidized at about 90° C. forabout 4 hours. The thus-obtained imide was dissolved in DMAc(dimethylacetamide), and then Pd/C was added thereto to prepare amixture. The resulting mixture was reduced at 45° C. under hydrogenpressure of 6 bar for 20 minutes to prepare diamine DA-1.

Production Example 1-2) Synthesis of Diamine DA-2

DA-2 having the above structure was produced in the same manner as inProduction Example 1-1, except that cyclobuthane-1,2,3,4-tetracarboxylicdianhydride (CBDA) was used instead of1,3-dimethylcyclobuthane-1,2,3,4-tetracarboxylic dianhydride.

Production Example 2: Production of Polymer for Liquid Crystal AligningAgent Production Example 2-1) Production of Polymer for Liquid CrystalAligning Agent P-1

(Step 1)

5.0 g (13.3 mmol) of DA-2 produced in Production Example 1-2 wascompletely dissolved in 71.27 g of anhydrous N-methyl pyrrolidone (NMP).Then, 2.92 g (13.03 mmol) of1,3-dimethyl-cyclobuthane-1,2,3,4-tetracarboxylic dianhydride (DMCBDA)was added to the solution under an ice bath and stirred at roomtemperature for 16 hours.

(Step 2)

The solution obtained in Step 1 was poured into an excess amount ofdistilled water to form a precipitate. Then, the formed precipitate wasfiltered and washed twice with distilled water and again three timeswith methanol. The thus-obtained solid product was dried in a vacuumoven at 40° C. for 24 hours to obtain 6.9 g of a polymer for a liquidcrystal aligning agent P-1.

As a result of confirming the molecular weight of P-1 through GPC, thenumber average molecular weight (Mn) was 15,500 g/mol, and the weightaverage molecular weight (Mw) was 31,000 g/mol. Further, the monomerstructure of the polymer P-1 was determined by the equivalent ratio ofthe monomers used, and the ratio of imine structure in the molecule was50.5%, while the ratio of amic acid structure was 49.5%.

Production Example 2-2) Production of Polymer for Liquid CrystalAligning Agent P-2

5.0 g of DA-1 produced in Production Example 1-1 and 1.07 g ofp-phenylenediamine (PDA) were completely dissolved in 103.8 g of NMP.Then, 2.12 g of cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA)and 3.35 g of 4,4′-oxydiphthalic dianhydride (OPDA) were added to thesolution under an ice bath and stirred at room temperature for 16 hours.The polymer P-2 was then produced in the same manner as in Step 2 ofProduction Example 2-1.

As a result of confirming the molecular weight of P-2 through GPC, thenumber average molecular weight (Mn) was 18,000 g/mol, and the weightaverage molecular weight (Mw) was 35,000 g/mol. Further, as for thepolymer P-2, the ratio of the imine structure in the molecule was 36.4%,and the ratio of the amic acid structure was 63.6%.

Production Example 2-3) Production of Polymer for Liquid CrystalAligning Agent P-3

6.0 g of DA-2 produced in Production Example 1-2 and 1.37 g of4,4′-oxydianiline (ODA) were completely dissolved in 110.5 g of NMPThen, 3.47 g of DMCBDA and 1.44 g of pyromellitic dianhydride (PMDA)were added to the solution under an ice bath and stirred at roomtemperature for 16 hours. The polymer P-3 was then produced in the samemanner as in Step 2 of Production Example 2-1.

As a result of confirming the molecular weight of P-3 through GPC, thenumber average molecular weight (Mn) was 14,500 g/mol, and the weightaverage molecular weight (Mw) was 29,000 g/mol. Further, as for thepolymer P-3, the ratio of the imide structure in the molecule was 41.9%,and the ratio of the amic acid structure was 58.1%.

Production Example 2-4) Production of Polymer for Liquid CrystalAligning Agent Q-1

5.00 g of 4,4′-methylenedianiline and 5.05 g of 4,4′-oxydianiline werecompletely dissolved in 221.4 g of NMP. Then, 14.55 g of 4,4′-biphthalicanhydride was added to the solution under an ice bath and stirred atroom temperature for 16 hours. The polymer Q-1 was then produced in thesame manner as in Step 2 of Production Example 2-1.

As a result of confirming the molecular weight of Q-1 through GPC, thenumber average molecular weight (Mn) was 25,000 g/mol, and the weightaverage molecular weight (Mw) was 40,000 g/mol.

Examples: Production of Liquid Crystal Aligning Agent CompositionExample 1

5 parts by weight of P-1 produced in Production Example 2-1, 5 parts byweight of Q-1 produced in Production Example 2-4, 0.5 part by weight of(3′,4′-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (Celloxide2021P manufactured by Daicel), and 0.5 parts by weight of phosphine(PH₃) were completely dissolved in a mixed solvent of NMP andn-butoxyethanol in a weight ratio of 8:2. Then, the resultant wassubjected to pressure filtration with a filter made ofpoly(tetrafluoroethylene) having a pore size of 0.2 μm to produce aliquid crystal aligning agent composition.

Example 2

A liquid crystal aligning agent composition was produced in the samemanner as in Example 1, except that P-2 produced in Production Example2-2 was used instead of P-1 produced in Production Example 2-1.

Example 3

A liquid crystal aligning agent composition was produced in the samemanner as in Example 1, except that P-3 produced in Production Example2-3 was used instead of P-1 produced in Production Example 2-1.

Example 4

A liquid crystal aligning agent composition was produced in the samemanner as in Example 3, except that trimethyl phosphine was used insteadof phosphine.

Comparative Example: Production of Liquid Crystal Aligning AgentComposition Comparative Example 1

A liquid crystal aligning agent composition was produced in the samemanner as in Example 1, except that phosphine was not used.

Comparative Example 2

A liquid crystal aligning agent composition was produced in the samemanner as in Example 1, except that Celloxide 2021P was not used.

Comparative Example 3

A liquid crystal aligning agent composition was produced in the samemanner as in Example 1, except that Q-1 produced in Production Example2-4 was used instead of P-1 produced in Production Example 2-1.

Experimental Example 1

1) Production of Liquid Crystal Cell

A liquid crystal cell was produced by using the liquid crystal aligningagent compositions prepared in the examples and comparative examples.

Specifically, the liquid crystal aligning agent composition produced inthe examples and comparative examples was coated onto a substrate (lowerplate) in which comb-shaped IPS (in-plane switching) mode ITO electrodepatterns having a thickness of 60 nm, an electrode width of 3 μm, and aspacing between electrodes of 6 μm were formed on a rectangular glasssubstrate having a size of 2.5 cm×2.7 cm and onto a glass substrate(upper plate) having no electrode pattern each using a spin coatingmethod.

Then, the substrates onto which the liquid crystal aligning agentcomposition was coated were placed on a hot plate at about 70° C. for 3minutes to evaporate the solvent. In order to subject the thus-obtainedcoating film to alignment treatment, ultraviolet rays of 254 nm wereirradiated with an intensity of 1 J/cm² using an exposure apparatus inwhich a linear polarizer was adhered to the coating film of each of theupper and lower plates.

Thereafter, the coating film was calcinated (cured) in an oven at about230° C. for 30 minutes to obtain a coating film having a thickness of0.1 μm. Then, a sealing agent impregnated with a ball spacer having asize of 3 μm was applied to the edge of the upper plate excluding theliquid crystal injection hole. Subsequently, the alignment films formedon the upper plate and the lower plate were aligned such that they facedeach other and the alignment directions were aligned with each other,and then the upper and lower plates were bonded together and the sealingagent was cured to prepare an empty space. Then, a liquid crystal wasinjected into the empty cells to produce an IPS mode liquid crystalcell.

2) Evaluation of Liquid Crystal Alignment Properties

Polarizers were attached to the upper and lower substrates of the liquidcrystal cell produced by the above method so that they were vertical toeach other. The polarizer-attached liquid crystal cell was then placedon a backlight with brightness of 7000 cd/m², and light leakage wasobserved with the naked eye. At this time, if the alignment propertiesof the liquid crystal alignment film are excellent and the liquidcrystal is arranged well, light is not passed through the upper andlower polarizing plates attached vertically to each other, and it isobserved as dark without defects. In this case, the alignment propertieswere evaluated as ‘good’, and when light leakage such as liquid crystalflow mark or bright spot is observed, it was evaluated as ‘poor’. Theresults are shown in Table 1 below.

3. Evaluation of Alignment Film Strength

The alignment films obtained from the liquid crystal aligning agentcompositions produced in the examples and comparative examples weresubjected to rubbing treatment while rotating the surface of thealignment film at 850 rpm using a rubbing machine (SHINDO Engineering),and then the haze value was measured using a haze meter. The differencebetween the haze value after rubbing treatment and the haze value beforerubbing treatment was calculated as shown in the following Equation 1 toevaluate the film strength. If the change in haze values is less than 1,it was evaluated that the film strength is excellent.

Film strength (%)=Haze of the liquid crystal alignment film afterrubbing treatment (%)−Haze of the liquid crystal alignment film beforerubbing treatment (%)  [Equation 1]

Experimental Example 2

1) Production of Liquid Crystal Cell

A liquid crystal cell was produced in the same manner as in ExperimentalExample 1, except that a step of placing the coating film on a hot plateat 130° C. for 500 seconds to perform a low-temperature heat treatmentis further included, before calcinating (curing) the coating film in anoven at about 230° C. for 30 minutes.

TABLE 1 Results of measurement of the examples and comparative examplesComparative Comparative Comparative Class Example 1 Example 2 Example 3Example 4 Example 1 Example 2 Example 3 Polymer Production ProductionProduction Production Production Production Production Example 2-1Example 2-2 Example 2-3 Example 2-3 Example 2-1 Example 2-1 Example 2-4Production Production Production Production Production ProductionExample 2-4 Example 2-4 Example 2-4 Example 2-4 Example 2-4 Example 2-4Epoxy Celloxide Celloxide Celloxide Celloxide Celloxide — Celloxideadditive 2021P 2021P 2021P 2021P 2021P 2021P Phosphine-based PhosphinePhosphine Phosphine Trimethyl — Phosphine Phosphine additive phosphineAlignment Good Good Good Good Good Good Poor properties Film 0.53 0.60.48 0.3 1.46 5 1.9 strength

As shown in Table 1, it was confirmed that the alignment film obtainedfrom the liquid crystal aligning agent compositions of Examples 1 to 4containing the polymer synthesized in Production Example 2-1 to 2-3, anepoxy additive, and a phosphine-based additive had excellent filmstrength and alignment properties.

On the other hand, it was confirmed that the alignment film obtainedfrom the liquid crystal aligning agent compositions of ComparativeExample 1 containing no phosphine-based additive was remarkably poor infilm strength as compared with the examples.

In addition, it was confirmed that the alignment film obtained from theliquid crystal aligning agent compositions of Comparative Example 2containing no epoxy additive was remarkably poor in film strength ascompared with the examples.

Further, it was confirmed that the alignment film obtained from theliquid crystal aligning agent compositions of Comparative Example 3containing no polymer synthesized in Production Example 2-1 wasremarkably poor in alignment properties as compared with the examples.

Accordingly, it was confirmed that when the polymer synthesized inProduction Example 2-1, the epoxy additive, and the phosphine-basedadditive were simultaneously contained in the liquid crystal aligningagent composition as in the examples, the physical properties of theliquid crystal alignment film could be remarkably improved.

1. A liquid crystal aligning agent composition comprising: i) a firstpolymer for a liquid crystal aligning agent including two or morerepeating units selected from the group consisting of a repeating unitrepresented by Chemical Formula 1, a repeating unit represented byChemical Formula 2, and a repeating unit represented by Chemical Formula3, wherein the first polymer includes the repeating unit represented byChemical Formula 1 in an amount of 5 mol % to 74 mol % with respect to atotal of the repeating units represented by the following ChemicalFormulae 1 to 3, ii) a second polymer for a liquid crystal aligningagent including a repeating unit represented by Chemical Formula 4, iii)a compound having two or more epoxy groups in a molecule, and iv) aphosphine-based compound represented by Chemical Formula 5:

wherein, in Chemical Formulae 1 to 5, at least one of R¹ and R² is aC₁₋₁₀ alkyl, and the rest is hydrogen, R³ and R⁴ are each independentlyhydrogen or a C₁₋₁₀ alkyl, A¹, A², and A³ are each independentlyhydrogen, a C₁₋₂₀ alkyl, a C₃₋₂₀ cycloalkyl, a C₆₋₂₀ aryl, or a C₆₋₂₀aryl substituted with at least one C₁₋₂₀ alkyl group, X¹ is atetravalent organic group represented by Chemical Formula 6, X², X³, andX⁴ are each independently a tetravalent organic group derived from ahydrocarbon having 4 to 20 carbon atoms, or a tetravalent organic groupin which at least one H in the tetravalent organic group is substitutedwith a halogen, or at least one —CH₂— is replaced by —O—, —CO—, —S—,—SO—, —SO₂—, or —CONH— such that oxygen or sulfur atoms are not directlylinked, and

wherein, in Chemical Formula 6, R⁵ to R⁸ are each independently hydrogenor a C₁₋₆ alkyl, Y¹, Y², Y³, and Y⁴ are each independently a divalentorganic group represented by Chemical Formula 7,

wherein, in Chemical Formula 7, R⁹ and R¹⁰ are each independently ahalogen, a cyano, a C₁₋₁₀ alkyl, a C₂₋₁₀ alkenyl, a C₁₋₁₀ alkoxy, aC₁₋₁₀ fluoroalkyl, or a C₁₋₁₀ fluoroalkoxy, p and q are eachindependently an integer between 0 and 4, and L¹ is a single bond, —O—,—CO—, —S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂—, —CONH—, —COO—, —(CH₂)_(z)—,—O(CH₂)_(z)O—, —O(CH₂)_(z)—, —OCH₂—C(CH₃)₂—CH₂O—, —COO—(CH₂)_(z)—OCO—,or —OCO—(CH₂)_(z)—COO—, wherein z is an integer between 1 and 10, m isan integer between 0 and
 3. 2. The liquid crystal aligning agentcomposition of claim 1, wherein in the Chemical Formula 5, A¹, A², andA³ are each independently hydrogen or a C₁₋₃ alkyl.
 3. The liquidcrystal aligning agent composition of claim 1, wherein thephosphine-based compound is included in an amount of 0.03 parts byweight to 30 parts by weight based on a total of 100 parts by weight ofthe first polymer for the liquid crystal aligning agent and the secondpolymer for the liquid crystal aligning agent.
 4. The liquid crystalaligning agent composition of claim 1, wherein the X², X³, and X⁴ areeach independently a tetravalent organic group represented by ChemicalFormula 8:

wherein, in Chemical Formula 8, R¹¹ to R¹⁴ are each independentlyhydrogen or a C₁₋₆ alkyl, and L² is a single bond, —O—, —CO—, —S—,—C(CH₃)₂—, —C(CF₃)₂—, —CONH—, —COO—, —(CH₂)_(z)—, —O(CH₂)_(z)O—, or—COO—(CH₂)_(z)—OCO—, wherein z is an integer between 1 and
 10. 5. Theliquid crystal aligning agent composition of claim 1, wherein a weightratio between the first polymer for a liquid crystal aligning agent andthe second polymer for a liquid crystal aligning agent is 1:9 to 9:1. 6.The liquid crystal aligning agent composition of claim 1, wherein themolecular weight of the compound having two or more epoxy groups in amolecule is 100 g/mol to 10,000 g/mol.
 7. The liquid crystal aligningagent composition of claim 1, wherein the compound having two or moreepoxy groups in a molecule is a cycloaliphatic-based epoxy, abisphenol-based epoxy, or a novolac-based epoxy.
 8. The liquid crystalaligning agent composition of claim 1, wherein the compound having twoor more epoxy groups in a molecule is included in an amount of 0.1 partsby weight to 30 parts by weight based on a total of 100 parts by weightof the first polymer for a liquid crystal aligning agent and the secondpolymer for a liquid crystal aligning agent.
 9. A method for producing aliquid crystal alignment film comprising the steps of: 1) coating theliquid crystal aligning agent composition of claim 1 onto a substrate toform a coating film; 2) drying the coating film; 3) subjecting thecoating film to alignment treatment immediately after the drying step;and 4) heat-treating and curing the alignment-treated coating film. 10.The method for producing a liquid crystal alignment film of claim 9,wherein the liquid crystal aligning agent composition is dissolved ordispersed in an organic solvent.
 11. The method for producing a liquidcrystal alignment film of claim 9, wherein the drying of Step 2 isperformed at a temperature of 50° C. to 130° C.
 12. The method forproducing a liquid crystal alignment film of claim 9, wherein thealignment treatment of Step 3 is performed by irradiating polarizedultraviolet rays having a wavelength of 150 nm to 450 nm.
 13. The methodfor producing a liquid crystal alignment film of claim 9, wherein Step 4comprises the steps of: 4-1) subjecting the alignment-treated coatingfilm to a low-temperature heat treatment at 200° C. or less; and 4-2)heat-treating and curing the heat-treated coating film at a temperatureof higher than that of the low-temperature heat treatment.
 14. Themethod for producing a liquid crystal alignment film of claim 13,wherein the low-temperature heat treatment of Step 4-1 is performed at atemperature of 110° C. to 200° C.
 15. The method for producing a liquidcrystal alignment film of claim 13, wherein the heat treatment of Step4-2 is performed at a temperature of 200° C. to 250° C.
 16. A liquidcrystal alignment film comprising an aligned and cured product of theliquid crystal aligning agent composition of claim
 1. 17. A liquidcrystal display device comprising the liquid crystal alignment film ofclaim 16.